The present invention relates to an extraction or extractive furnace for extracting gaseous components from material samples, for example metallic samples or nonmetallic samples such as ceramics, such extracted gaseous components then being analyzed in various known manners. More specifically, the present invention relates to such a furnace whereby a crucible formed of an electrically conductive material, for example a graphite crucible, is positioned between and in electrical contact with an upper electrode and a lower electrode, with an electric current being applied between such electrodes, with the result that the material sample is made molten or is dissolved due to Joule's heat, whereby gaseous components of the material are extracted.
In known furnaces of this general type, the condition of the surfaces of mutual contact between the crucible and the upper and lower electrodes is directly expressed by an electric contact resistance and significantly influences the extractive temperature, and this often may lead to inaccuracy of analysis of the gaseous components. Consequently, it is desired to ensure the best possible electrical contact and the tightest possible contact between the crucible and the electrodes in order to achieve the most accurate possible analysis. However, after conducting a number of extraction operations, the surfaces of the electrodes are exposed to high temperatures and become oxydized, or the various samples splash onto and adhere to the surfaces of the electrodes. This leads to the prevention of a tight and close electrical contact between the material of the electrodes and the crucible.
In the past it has been considered a suitable solution to such problem to polish or clean the surfaces of the electrodes, for example by a mechanical cleaning of the contact surfaces by means of abrasive papers, brushes or the like, before or after an analysis operation. This however is a time consuming and troublesome operation. In addition, there is the possibility that excess polishing or cleaning will lead to a premature deterioration of the contact surfaces of the electrodes.